1. Field of the Invention
The present invention relates to a positive electrode for a nonaqueous secondary battery and a method for forming the positive electrode. Further, the present invention relates to a nonaqueous secondary battery and an electrical device including the nonaqueous secondary battery.
2. Description of the Related Art
In recent years, a variety of power storage devices, for example, secondary batteries such as lithium-ion secondary batteries, lithium-ion capacitors, and air cells have been actively developed. In particular, demand for lithium-ion secondary batteries with high output and high energy density has rapidly grown with the development of the semiconductor industry, for electrical devices, for example, portable information terminals such as mobile phones, smartphones, and laptop computers, portable music players, and digital cameras; medical equipment; next-generation clean energy vehicles such as hybrid electric vehicles (HEVs), electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs); and the like. The lithium-ion secondary batteries are essential as rechargeable energy supply sources for today's information society.
A lithium-ion secondary battery, which is one of nonaqueous secondary batteries and widely used due to its high energy density, includes a positive electrode including an active material such as lithium cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4), a negative electrode formed of a carbon material such as graphite capable of occlusion and release of lithium ions, a nonaqueous electrolyte solution in which an electrolyte formed of a lithium salt such as LiBF4 or LiPF6 is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate, and the like. A lithium-ion secondary battery are charged and discharged in such a way that lithium ions in the secondary battery move between the positive electrode and the negative electrode through the nonaqueous electrolyte solution and inserted into or extracted from the active materials of the positive electrode and the negative electrode.
A binder is mixed into the positive electrode or the negative electrode in order that the active materials can be bound or the active material and a current collector can be bound. Since the binder is generally an organic high molecular compound such as polyvinylidene fluoride (PVdF) which has an insulating property, the binder has extremely low electron conductivity.
Hence, by mixing a conductive additive such as acetylene black (AB) or graphite particles, the electron conductivity between the active materials or between the active material and the current collector can be improved. Thus, a positive electrode active material with high electron conductivity can be provided (see Patent Document 1).